Thousands of miles of pipelines of various kinds underlie the surface of both civilized and uncivilized countries, and are used for the transport, inter alia, of fluids such as drinking water, grey water, sewage, industrial waste streams, natural gas, gasoline, oil, and the like. Virtually all these types of pipelines are subject to leakage at some point, due, for example, to corrosion, rusting, or general decay of the pipeline walls, or from cracks or displacements due to shift of the earth around the pipeline, or its ground-mounted supports if located above ground. If the pipelines are located above ground, or in rural areas, replacement of the pipeline or large sections thereof may be a possibility. However, in urban environments, particularly in large cites, replacement is a sometimes impossible and always exceptionally high priced operation. Hence, methods of relining existing pipelines have been developed to extend their service life at reasonable cost.
Several relining methods have been developed over the years. All share several technological features: a flexible liner having a maximum dimension considerably less than the pipeline inside diameter is inserted into the pipeline, expanded to contact the pipeline walls, and cured or allowed to harden in place. The cured (inclusive of "cured" and "hardened") liner must be impervious to the fluid being transported, and the liner must be sufficiently thick and strong to be substantially self-supporting in order to successfully reline areas of the pipeline exhibiting severe deterioration or having large cracks.
Liners may be categorized into two broad categories, thermoplastic liners and thermoset liners.
Thermoplastic liners are liners which are generally manufactured as a continuous extruded tube of heat-softenable polymer such as polyethylene, polypropylene, polybutylene, polyethylene terephthalate, polyvinylchloride (PVC), etc. These or other thermoplastics may be specially compounded to have lower than usual softening temperatures, or standard thermoplastics may be used. The thermoplastic liners, following extrusion, are folded transversely (across the diameter) into a "C" or other section whose maximum dimension is less than the nominal outside diameter of the liner, and wound into large reels. At the job site, hot air or stream is passed through the liner, or the entire reel of liner may be enclosed in a heated building, tent, or trailer, to soften the liner and render it flexible. The liner is then introduced into the pipe through a manhole or service hole, cleanout, etc., and pulled through the pipe. Alternatively, the extruded pipe may be flattened rather than folded and wound on a reel. At this job site, the flattened liner is folded, either by hand or by machine, prior to insertion into the pipeline.
When in place, hot air or steam under pressure is applied, and the folded pipe unfolds to contact the inside diameter of the pipe. Pressure is maintained until the liner has cooled below the softening point. These liners are flexible when sufficiently heated, despite being made of relatively rigid thermoplastic of large wall thickness. It is not unusual for a liner for a 10 inch (25.4 cm) inside diameter pipe to be about 0.375 inch (ca. 1 cm) in wall thickness. Preferably, a thermoplastic having some degree of shape memory is selected so that the unfolding of the liner to its circular cross-section shape is facilitated. However, a plug, mandrel, or like device may be pulled through the still soft liner to ensure that it has unfolded properly and makes good contact with the interior pipe wall. Manufacture and installation of thermoplastic liners may be illustrated with reference to U.S. Pat. Nos. 4,867,921; 5,071,616; 5,213,727; 5,346,658; 5,368,809; 5,810,053; 5,589,131; 5,385,173; and 5,342,570.
Thermoset liners are of several types. All have a fibrous tubular structure which is impregnated, either at the time of manufacture, just prior to insertion into the pipe, or following insertion, with a thermosetting or "crosslinkable" polymer or "resin". The thermosetting polymer may contain a thermally activated catalyst, may cure by interaction with hot steam, or may be photochemically cured. While various types of liners may be used, liners based on epoxy resins or unsaturated polyester resins are preferred, particularly the latter.
The thermosettable liners may be folded across their cross-section as with the thermoplastic liners and inserted into the pipeline. Alternatively, due to their greater inherent flexibility in the uncured state, the liners may be introduced into the pipeline by "eversion", wherein newly introduced liner is inserted into previously introduced liner and everted in the pipe. This method of introducing thermosettable liners, and may be illustrated by U.S. Pat. Nos. 5,010,440; 5,486,332; 5,597,353; and 5,653,555. The liner may also, due to is inherently greater flexibility than softened rigid liner, be inserted into the pipe in a flattened state or in other configurations.
Non-wireless communication, particularly in the form of coaxial cables, fiber-optic cables, and telephone cables containing numerous wires, has proliferated greatly in recent years. Fiber optic cables, in particular, are now being resorted to or contemplated for use in providing broadband digital communication paths. There are only limited opportunities to string such cables above ground in many areas. In highly urban environments, tunnels or dedicated conduits for use with telecommunications cables are limited in size, and may not be available in all locations where they are desired.
Since pipelines have enormous geographical distribution, it would be desirable if they could be used to house telecommunications cables. Unfortunately, this is generally possible only when the pipeline has been freed from other use. One method which has been suggested to provide for cables located within a liquid or gas transport pipeline is to traverse the pipeline with a robot which mounts `J" hooks in the topmost portion of the pipeline, the cable being supported by and between these J hooks. This method has several disadvantages, however. Not only is the cable in direct contact with the pipeline contents, but due to the installed hooks, the pipeline may no longer cleaned or refurbished by conventional means. Unless properly sealed, the points of installation of hooks may cause leakage. This method has required unusually rigid cables with special forms of insulation and cable jackets.
In U.S. Pat. No. 5,395,472, a dual leakage containment system is disclosed wherein into the original pipeline are inserted two concentric liners with spacings in-between. The spacing are said to be useable for leak detection sensors. However, the use of two concentric liners, particularly those having a space therebetween, is not only double expensive, but also severely limits the useable cross-sectional area of the pipeline. Thus, fluid carrying capacity is diminished. Moreover, should a leak occur in the interior liner, all leak detection cables will be exposed to the fluid being transported. As indicated previously, it is generally undesirable to have cables, particularly at connection or splice points, to be in contact with liquid environments due to signal loss and to extraction of stabilizers from the cable insulation, which may result in premature failure.
It would be desirable to provide the ability to employ the presently existing, huge pipeline infrastructure for telecommunications use without necessarily abandoning the original function of the pipeline, and without exposure of the telecommunications cables to adverse environments, for example the pipeline interior surface, or liquids contained purposefully within the pipeline or those which may infiltrate between a pipeliner and the pipeline proper.